Ecotoxicological Pathways Overlooked: a Critical Evaluation of the Baseline Ecological Risk Assessment and Potential Natural Resource Injury from Libby Amphibole Asbestos.

Libby amphibole asbestos (LAA) remains a persistent source of environmental exposure within Operable Unit 3 (OU3) of the Libby Asbestos Superfund Site. This review evaluates ecological evidence relevant to OU3, including the U.S. EPA's Baseline Ecological Risk Assessment (BERA), published toxicology studies, fiber-burden data, and recent federal actions under the Toxic Substances Control Act (TSCA). BERA provided valuable initial information but did not evaluate many endpoints now recognized as sensitive indicators of asbestos-related injury, including immune disruption, early physiological stress, altered behavior, genomic and epigenetic changes, and subclinical effects in longer-lived wildlife. Several exposure pathways, including soil, sediment, vegetation, prey species, and trophic transfer, were incompletely assessed. Fiber-burden analyses in OU3 fish confirm biologically relevant exposure, and findings from amphibole-exposed laboratory animals examining respiratory injury, oxidative stress, growth impairment, and altered immune function, indicate that these injury pathways are plausible in wild species. Recent TSCA risk evaluations remain focused on human health and exposures, with minimal treatment of ecological pathways. This regulatory gap parallels the scientific limitations of the BERA and highlights the need for modernized ecological assessment tools. Evidence from other asbestos-impacted regions underscores that these issues are not unique to Libby; legacy amphibole fiber contamination continues to affect soils, sediments, vegetation, and wildlife elsewhere. The collective evidence indicates a reasonable probability that LAA is affecting natural resources in OU3 through both direct and indirect mechanisms.